1. Field of the Invention
The present invention relates generally to an optical apparatus for producing three dimensional (3D) photographs, and more specifically to a 3D printer which projects a set of 2D images onto a lenticular-type material to form a composite 3D photograph.
2. Prior Art
In lenticular-type three dimensional (3D) photography, the basic process involves taking a plurality of two dimensional (2D) views from a number of horizontally-spaced vantage points, and compressing these 2D views onto each of the lenticules of a lenticular screen to form a 3D composite image of the scene. The lenticular screen is a sheet of transparent material with the front side embossed with an array of cylindrical lenses with the backside coated with a photosensitive layer or the lenses can be attached to photographic film or paper. The 2D views are captured by a camera which exposes a number of frames onto photographic film. The basic process of producing a lenticular-type 3D photograph from a set of 2D frames has been discussed in detail in a number of books and patent disclosures. For example, L. Dudley discussed in "Applied Optics and Optical Engineering" (R. Kingslake, Ed., 1965) a printing method where the lenticular screen is transported intermittently so that each of the eight 2D images recorded on film is exposed at different angles; T. Okoshi discussed in "Three-Dimensional Imaging Techniques" (1978) the use of several projectors to expose a plurality of 2D images onto the photographic emulsion; U.S. Pat. No. 3,482,913 (Glenn) discloses a method of using a number of projectors for composing 3D photographs; U.S. Pat. No. 3,895,867 (Lo et al.) discloses a technique of recording images on all of the film areas underlying the lenticules with intermittent exposure and shifting of the print material; U.S. Pat. No. 4,120,562 (Lo et al.) discloses a scanning means for exposing a number of 2D images at different projection angles; U.S. Pat. No. 4,101,210 (Lo et al.) discloses a method of filling the film area underlying the lenticules by using a plurality of projection lenses; N. A. Valyus discussed in "Stereoscopy" (Focal Press, 1966) the importance of having proper registration of an image to obtain the 3D effect; U.S. Pat. No. 4,903,069 (Lam) discloses an apparatus and method of putting a machine readable code on the negative film so that registration of images can be carried out automatically; U.S. Pat. No. 5,028,950 (Fritsch) discloses a dual-stage 3D printer in which the exposure of 2D images onto the print material is carried out in a printing station while the computation for image registration and color adjustment is carried out in a separate editing station.
When composing a 3D photograph, two basic procedures must be carried out to insure a good result: 1) the selection of the key subject on an image, and 2) the alignment of key subject in each view. U.S. Pat. No. 3,895,867 (Lo et al) discloses a method of printing in which each negative is visually examined to select an object which will become the center plane of the 3D picture. The selected object is known as the key subject. The key subject in the photographed scene on each of the 2D views must be accurately registered on the lenticular print material in order to produce an in-focus 3D image, which is one of the most important steps in producing lenticular-type 3D photographs. In the past, the alignment of key subject is done manually. As mentioned in U.S. Pat. No. 4,903,069 (Lam), the alignment is carried out during the printing process by an operator who uses cross-hairs to register the key subject on the print material while viewing through an optical device.
U.S. Pat. No. 5,028,950 (Fritsch) mentions the use of a CCD video camera (without a lens) to capture the key subject of the first 2D image and place the information in digital memory (frame grabber), to be electronically combined with the key subject of the second frame. The operator uses a controller to move the film to bring the key subject in the second frame into registration with the stored location of the first frame while using the combined image as a guide.
The aforementioned manual methods for aligning the key subject of each view is time-consuming and relies heavily on the operator's skill and performance. It is desirable to implement an image comparison scheme so that key subject in each view can be automatically aligned.
In the past, some pattern comparison or image matching schemes have been mentioned in a number of patents. U.S. Pat. No. 4,903,069 (Lam) mentions using an image recognition device when printing 2D views taken by a multi-lens camera without having special codes imprinted on the negative. As mentioned, a video camera is used to view the key subject image of the first 2D frame and the view is digitized and stored by an image grabber for reference. After the first 2D frame is exposed onto the print material, the second 2D frame is transported to the approximated location of the first 2D frame. The video camera then compares the key subject image of the second 2D frame with the information of the first 2D view captured by the image grabber. Subsequently, the second 2D view is then registered to the first 2D view by an XY positioning device.
U.S. Pat. No. 5,028,950 (Fritsch) discloses a dual-stage 3D printer in which frame-to-frame registration data are produced electronically using a sophisticated image-processing system. In the disclosed dual-stage 3D printer, a CCD video camera with a 480.times.512 pixel array is used to capture the image on the negative and present it to the operator for key subject designation. Within the same video image, an area of 28.times.28 pixels is used by an auto registration computer to do correlation search on an image of 55.times.95 pixels (or larger area if necessary) from other frames in order to find the key subject location.
U.S. Pat. No. 5,036,356 (Lo) mentioned a method for the automatic correlation of 2D views in composing high quality 3D photographs. In a camera preloaded with photographic film, it is possible to take the first set of 2D photographs on the film of a target at a predetermined distance. In the mentioned method, the target images are projected onto a single CCD array or a group of CCD sensor arrays placed at the image plane of the printer with each individual sensor of the CCD array precalibrated. A computer on the printer is programmed to recognize the location of the target images on the CCD array. With the location of each target image known, the position of the enlarging lens or the easel on which the print material rests or the 2D negative can be adjusted so that the multiple frame images can be aligned. Invariably, these disclosures use a video camera or one or more CCD arrays to digitize the 2D images, and a computer to find the location of the key subject or target image in each frame.
Mathematically, the relative locations of the key subject in each frame can be accurately computed. In practice, there are two major disadvantages: 1) it will takes a considerable amount of time to compute the relative locations of the key subject in all 2D frames, and 2) the key subject registration carried out by mechanical means is not always accurate. In particular, in the dual-stage printing method disclosed by U.S. Pat. No. 5,028,950 (Fritsch) where key subject comparison is carried out on one mechanical stage while the actual alignment of key subject is carried out on another mechanical stage, good alignment is not always insured. Furthermore, in the dual-stage design where a long slack loop assembly is used to allow time differences between editing and printing, there will be a sufficiently long time elapsed between a set of negatives to be edited and the same set of negatives to be exposed for printing. The heating by the lamphouse in the editing station and the humidity in the air can distort the film. Consequently, the relative locations of the key subject at the time of printing may not be the same as those at the time of editing. This distortion on the film could add to the error in the final key subject registration on the photograph.
Thus, it is desirable to compose the 3D photograph in a single-stage printer where the optics for key subject comparison and the optics for printing are assembled on the same mechanical stage, and the printing is carried out immediately after the key subject alignment is completed. Moreover, in the dual-stage printer design, one video camera is used for both taking the full frame image for key subject designation and for acquiring image data for key subject alignment, without changing the optics of the camera. Such approach produces unacceptable errors in key subject registration on the 3D photographs. Furthermore, when different lamphouses are used for editing and printing, color balancing becomes a much more complex task.